This invention relates to forming a drive center of the scroll members to be offset from the origin of the wraps, to reduce or eliminate torque reversal.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a pair of scroll members each have a base and a generally spiral wrap interfitting to define compression chambers. One of the two scroll members is caused to orbit relative to the other, and as a result of this action, the compression chambers are reduced in volume, thereby compressing an entrapped refrigerant. An anti-rotation coupling facilitates the orbiting movement of the orbiting scroll.
Historically, scroll wraps were formed as an involute of a circle. More recently, more complex shapes involving a combination of curves, involutes, and other shapes have been utilized to form a so-called xe2x80x9chybrid wrap.xe2x80x9d Each type of wrap, including traditional involutes of circles, is generated from an origin point which has typically also been the drive center of the scroll member.
Hybrid wraps provide a variety of improvements to the operation and efficiency of a scroll compressor. However, one challenge raised by a hybrid wrap is that they may sometimes generate torque reversal in the anti-rotation coupling. Thus, over a small portion of the rotation angle of the drive shaft, there can be reverse torque being applied by the orbiting scroll to the anti-rotation coupling. This can be undesirable, and can result in excess noise or vibration.
One technique that has been utilized by scroll compressor designers in the past to achieve a reduced size is to offset the wrap origins relative to the drive centers. In particular, the orbiting scroll typically has a boss extending downwardly which receives a drive bearing. An eccentric from the drive shaft extends upwardly into this drive bearing. The drive center of the orbiting scroll could be defined as the center of this boss or bearing. In the past, the origin upon which the orbiting scroll wrap is generated, has been offset from this drive center to result in a smaller housing size. At the same time, the non-orbiting scroll is also offset in the same direction and by the same amount relative to its drive axis, which is typically the center of the drive shaft. Again, this technique has been proposed to achieve a smaller housing size, and as often as not, would actually increase the torque reversal problem mentioned above. Also, it is not believed this technique has been proposed on a hybrid wrap.
In the disclosed embodiment of this invention, an offset is identified which results in the elimination or reduction of torque reversal, and also smoothes out torque fluctuations during the orbiting cycle of the orbiting scroll.
In a preferred embodiment of this invention, the torque versus drive angle amounts are plotted. A designer looks for the extremes in this torque function. An offset is defined to eliminate these extremes. In general, by finding the lowest negative torque amount, and thus the point of greatest torque reversal, the designer can determine the direction in which to design the offset. In particular, at the angular point of the lowest negative torque, the eccentric is spaced in a particular direction relative to the axis of the drive shaft. It is this direction in which the offset of the orbiting scroll wrap relative to its drive axis should be made. If the selected point is a negative torque point, then one would move the origin of the orbiting wrap more towards the shaft center. On the other hand, if the highest torque point is selected, then you would move the origin of the orbiting wrap away from the shaft center at that location.
By so moving the orbiting wrap origin relative to the drive and shaft centers, a generally sinusoidal function should be placed over the original or nominal torque function that will smooth out extremes, and eliminate torque reversal.